>To clarify, destination MTA != relay, right? According to your logs, >the problem (lost connection) occurs with the relay on port 24.
The relay is not being used as I push out to the primary via port 24 which is not blocked by the ISP. As a result, the backup mx communicates directly with the primary postfix mta with only assp proxying. I ruled anything assp might be doing as a first attempt by stopping the proxy and moving smtpd to port 25. >>If this doesn't prove useful I will attempt a tcpdump. > >Suit yourself. But using tcpdump to capture the packets is a trivial >exercise; no harm in trying it. And make sure to do so on the email (it >should be re-tried by Postfix if it's sitting in the queue) that is >causing the problem. Just because other test emails get through does >not rule out a problem. And yes, what software the relay MTA runs is >relevant; especially if this software does not properly implement SMTP. I would be supremely grateful for any guidance on that task, I have never captured/viewed smtp data and wouldn't know how to interpret it and filter out the session of interest! Thanks so much for the help! jlc
